This invention relates generally to coherent jet technology.
A recent significant advancement in the field of gas lancing is the development of the coherent jet technology disclosed, for example, in U.S. Pat. No. 5,814,125xe2x80x94Anderson et al. and in U.S. Pat. No. 6,171,544xe2x80x94Anderson et al. In the practice of this technology one or more high velocity gas jets ejected from one or more nozzles on a lance are maintained coherent over a relatively long distance by the use of a flame envelope around and along the high velocity gas jet(s). The flame envelope is formed by combusting fuel and oxidant ejected from the lance respectively from two rings of offset ports, an inner ring and an outer ring, around the high velocity gas jet nozzle(s). Typically the fuel for the flame envelope is ejected from the inner ring of ports and the oxidant for the flame envelope is ejected from the outer ring of ports. An extension on the lance perimeter forms a protected recirculation zone into which the high velocity gas jet(s) and the flame envelope fluids are provided from the nozzle(s) and ports. This recirculation zone enables some recirculation of the ejected fluids enabling improved ignition and improved stability of the flame envelope, thus enhancing the coherency and thus the length of the high velocity gas jet(s). The coherent jet(s) can be used to deliver gas into a liquid, such as molten metal, from a relatively long distance above the surface of the liquid. One very important application of this coherent jet technology is for providing oxygen for use in steelmaking operations such as electric arc furnaces and basic oxygen furnaces.
The recirculation extension, though constituting an improvement over earlier coherent jet systems, introduces certain problems concerning lance design and lance lifetime due to the need to water-cool the tip. These problems are of particular concern when the coherent jet system is used in a very harsh environment such as a basic oxygen furnace.
Accordingly, it is an object of this invention to provide a system which can produce effective coherent gas jets without the need for a lance extension or other element to establish a recirculation zone for the gases ejected from the lance.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for establishing at least one coherent gas jet comprising:
(A) passing at least one gas jet out from at least one nozzle housed in a lance having a lance face, said lance face having a first ring of ports around said at least one nozzle and a second ring of ports around said at least one nozzle and radially spaced from said first ring of ports, with each port of the second ring of ports aligned with a port of the first ring of ports;
(B) passing fuel out from one of the rings of ports and passing oxidant out from the other ring of ports, wherein the said at least one gas jet and the fuel and the oxidant are passed out from the lance directly into an injection volume without passing through a recirculation zone formed by an extension on the lance; and
(C) combusting the fuel and the oxidant passed out from the first and second rings of ports to produce a flame envelope around the said at least one gas jet.
Another aspect of the invention is:
A coherent jet lance comprising:
(A) a lance having a lance face and having at least one nozzle having an opening at the lance face and having no extension to form a recirculation zone adjacent the lance face;
(B) a first ring of ports around the nozzle opening(s) and a second ring of ports radially spaced from the first ring of ports around the nozzle opening(s), with each port of the second ring of ports aligned with a port of the first ring of ports; and
(C) means for providing fuel to one of the rings of ports and means for providing oxidant to the other ring of ports.
As used herein the term xe2x80x9clance face radiusxe2x80x9d means an imaginary line running from the center of a lance face to the perimeter of the lance face.
As used herein the term xe2x80x9calignedxe2x80x9d means intercepting the same lance face radius.
As used herein the term xe2x80x9cextensionxe2x80x9d means any structure, whether or not physically connected to a lance, which serves to form a protected volume or zone adjacent to the lance face.
As used herein the term xe2x80x9clance facexe2x80x9d means the surface of a lance abutting an injection volume.
As used herein the term xe2x80x9ccoherent jetxe2x80x9d means a gas jet which is formed by ejecting gas from a nozzle and which has a velocity and momentum profile along a length of at least 20d, where d is the exit diameter of the nozzle, which is similar to its velocity and momentum profile upon ejection from the nozzle. Another way of describing a coherent jet is a gas jet which has little or no change in its diameter for a distance of at least 20d.
As used herein the term xe2x80x9clengthxe2x80x9d when referring to a coherent gas jet means the distance from the nozzle from which the gas is ejected to the intended impact point of the coherent gas jet or to where the gas jet ceases to be coherent.